Diet restriction and exercise not only affect body weight but also have profound effects on body composition, metabolism and aerobic fitness. There is little agreement in the literature regarding the magnitude and direction of these changes. Literature reviews have summarized research using chronological arrangement or arrangement by subtopic which results in subjective and often non-replicable conclusions. This results in a lack of agreement regarding variables such as level and type of diet restriction, length of intervention, quality and quantity of exercise, magnitude of body weight changes, and how they contribute to the outcomes of body composition, fat distribution, metabolism, and aerobic fitness. The meta-analysis approach will be used to collect and analyze research on the relationships among variables associated with diet restriction, weight loss, body composition, fat distribution, metabolism, and aerobic fitness. Meta-analysis is a technique for pooling results of separate studies in a systematic, explicit, comprehensive, and replicable manner. It is a quantitative approach for increasing statistical power, resolving uncertainty when studies disagree, improving estimates of effect size, and answering questions that were not originally answered by the respective trials. The specific aims of this study are to: 1. statistically integrate and analyze existing research studies on the effects of energy restriction on weight loss, body composition, fat distribution, metabolism, and aerobic fitness; 2. determine the magnitude and direction of the changes in these variables in response to the degree of energy restriction; 3. determine interactions among weight loss, body composition, fat distribution, metabolism, and aerobic fitness resulting from various degrees of energy restriction, weight loss, gender, race, ethnicity, energy expenditure, and experimental design quality; 4. compare similar levels of energy restriction between groups which employed exercise and those which used energy restriction alone on the variables of weight loss, body composition, fat distribution, metabolism, and aerobic fitness; and compare studies which use energy restriction or exercise to produce similar energy deficit on the above variables; 5. determine the influence that the type of obesity shows for weight loss, body composition, fat distribution, metabolism, and aerobic fitness; and 6. compile a database regarding the effects of energy restriction and/or exercise as they affect weight loss, body composition, fat distribution, metabolism, and aerobic fitness that will be available to interested researchers and clinicians. The investigators state that this investigation should provide clarification of the utility of exercise and/or energy restriction and provide direction for future research.